Nickel and its compounds are naturally present in the earth's crust and are released to the environment due to natural processes. In Denmark, nickel was detected in 3362 of 6972 wells (1993–2002) and in 221 wells, the current drinking water limit at 20 μg Ni/l was exceeded. Nickel compounds release the nickel ion in the environment as well as in mammalian tissues, and the nickel ion is the determining factor for the systemic toxicity. Thus, toxicological effects can be considered together for the nickel compounds.

Absorption of nickel from drinking water is about 30% for fasting individuals and about 5% for non-fasting individuals. Nickel is a well-known skin and respiratory sensitizer. Following repeated oral exposure, the developing foetus is the critical target with consistent evidence of toxicity seen (rats) at dose levels from 2.2 mg Ni/kg bw/day (NOAEL 1.1 mg Ni/kg bw/day). A TDI of 5.5 μg Ni/kg bw/day can be estimated from this NOAEL by taking an uncertainty factor of 200 into account.

Allocating 10% of the TDI to exposure from drinking water, a quality criterion of 17–28 μg Ni/l can be estimated, assuming an average drinking water consumption of 2.3–1.4 litre/day for adults, thus confirming the validity of the current drinking water limit at 20 μg Ni/l in Denmark as well as in the EU. The similarities and differences in the derivation of the quality criterion of 20 μg Ni/l (rounded value) versus the current WHO drinking water guideline of 70 μg Ni/l will be discussed in the poster.